Annulus pressure refers to the pressure of the fluid in an annulus between a drill string and the wellbore wall. Conventional managed pressure drilling (“MPD”) technology controls the annulus pressure within tight predetermined pressure limits throughout the drilling process to avoid the loss of drilling fluid and the influx of formation fluid, as well as to maintain the stability of the wellbore. The pressure limits are defined by the formation pore pressure and the fracture pressure, which is sometimes as narrow as a few hundred pounds per square inch (“psi”).
The MPD technology controls the annulus pressure-while-drilling (“APWD”) by adjusting the back pressure and causing drilling to be either at balance or slightly over or under balance. Thus, as will be appreciated, the MPD technology may perform better when APWD data is received faster and/or more frequently. For example, the rapid transmission of APWD data may enable a user to predict a sudden pressure change during a drilling job with a narrow pressure window and to react accordingly.
The APWD is impacted by many factors including hydrostatic pressure, friction pressure, back pressure, mud rheological properties, flow rate, cutting movement, pipe movement, drill string configuration, fractures and washouts, drilling noise, mud pulsers, etc. The effects of these factors make the APWD data noisy and discontinuous. The APWD data typically has a data range from about 0 psi to about 30,000 psi. The data measurements may go up and down by about 50 psi within a few seconds or by several hundred psi within a minute.
The current speed for mud-pulse telemetry is a few (e.g., 5) bits per second. Transmitting the high sampling rate APWD data along with other drilling and formation evaluation data, therefore, may be challenging.